Combination centrifugal-turbine pump



March 3, 1959 L. C. ROTH 2,875,698

COMBINATION CENTRIF'UGAL-TURBINE PUMP Filed March 16, 1955 2Sheets-Sheet l March 3, 1959 I L. C. ROTH l CQMBINATIONCENTRIFUGALJURBINE PUMP Filed Maron 1e, 1955 2 Sheets-Sheet 2 INVENTOR.le@ C. fz,

BY )Luuk lazily/dm United States Patent() 2,875,698 i COMBINATION`CENTRIFUGAL-TURBINE PUMP LeojC. Roth, Moline, Ill., assigner to Roy E.Roth Company, Rock Island, Ill., a corporation of Illinois.` e

Application March 16, 1955, Serial No. 494,632 8 Claims. (Cl. 10S- 108)This invention relates to an improved form of combinationcentrifugal-turbine pump, and is particularly concerned withimprovements which impart to the pump the ability to pump liquids at ornear the boiling point.

`Propane is one of the many liquids with low boiling points. It has aboiling point of 40 F. and, atlordinary room or ambient temperatures,produces vapor pressures varying from 25 lbs. per sq. in. to 180 lbs.per sq. in. Anhydrous ammonia also boils at temperatures below normalambient temperatures and is commonly employed in refrigeration systemswhere `it is deliberately boiled for refrigeration.

This invention is concerned particularly with pumping the abovementioned liquids into storage and transport tanks and with the fillingof cylinders and the like.

The present invention is also concerned with the pumping of variousother liquids handled ator nearboiling point in` refineries, gasolineplants, chemical and petrochemical plants. Among these are butadiene,styrene, propane, butane, ethane, ammonia, water and various Watersolutions. Such liquids may be at boiling point by virtue of temperatureor vacuum conditions.

The invention is also concerned with pumping liquid refrigerants such asFreon, ammonia, methyl chloride, sulphur dioxide, and carbon dioxide inthe refrigeration process.

The invention is also concerned `with pumping l-ow temperature liqueedgases such as liquid oxygen, nitrogen, and argon into storage andtransporttanks and cylinders. i

A liquid at the boiling point is in a state where slight increases intemperature or slight decreases in pressure create an active boilingwhich produces vapor. It is obvious that it isimpossible to lift such aliquid from `a lower level `to the pump.` However, it is not so obviousthat, even with a static suction head, it is diicult to pump liquids inthis state unless the suction heads are so highas to prevent boilingofthe liquid within the pump. Undermany conditions these suction headsmust be so great as to be impractical.

` The turbine pump consisting of a vanedimpeller and annular passagewith a peripheral suctionentrance and vertical discharge outlet has`been found widely satisfactory for such applications with liquid suctionheads of `2 to 6 feet when operating at 1750 R. P. M., and suction headsof 4 to l2 feet when operating at 3500 R. P. M.

`The range given at each speed is due to the individual characteristicsof speciiic models.

Basic turbine pump design is such that the impeller can be located torun free of contact with the side plates and water block. Also due tothe repeated impulses provided by the vanes of the impeller there is agradual pressure build-up which counteracts any increased vaporpressures caused by eiliciency losses. This has resulted in the wide useof this design for high pressure handling of non-lubricating liquids.

However, bel-ow the minimum suction heads indicated above, there is aphenomena encountered peculiar to turbine pumps. Partly due to suctionentrance pressure losses and partly due to internal by-pass of highpressure liquid a gradual increase in vapor building up occurs with theprogressive lowering of the suction head until at heads of 1 to 3 feetat 1750 R. P. M., and 2 to 6 2,875,698' Patented Mar. 3, 1959 ICC feetat 3500 R.. P. M. a complete vapor lock occurs within the pump.

Many instances are found in industry where it is essential topumpliquids at boiling point with suction heads of l foot or less. Atpresent, standard designs, turbine or otherwise, cannot till this need.Previous designs involving use of rotary gear or rotary vane pumps inconjunction with centrifugal stage arenot suitable-for non-lubricatingliquids and have a limited life in all liquids because of the metalliccontact of the gears or vanes.

It is also desirable to provide pumping equipment to handle boilingliquids with l foot suction head that can operate at conventional speedsfor electric motorsnamely 1750 and 3500 R. P. M. permitting directelectric motor drives. e

Accordingly, the present invention provides a special mechanical deviceintroducing preliminary to the `turbine pump and running at the samespeed which will provide a mechanical equivalent` to the minimumliquidsuction heads previously indicated.

In a turbine pump there are two principal factors which cause the activeboiling of the liquid and producey sufficient vapor to make the pumpvapor bind or stop pumping. One is a condition in which the pumpedliquid, such as a refrigerant, is at a very low temperature and is stillat the boiling point. In this case,lthe heat transferred through thepump casing from the ambient temperature outside causes the liquid toboil and produces vapor, even when the pump is at rest. Another fact-oris that the regenerative turbine action of the turbinepump adds heat tothe liquid, and some of this superheated liquid is carried over into thepump suction, where it ashes into a vapor, vapor binding the pump.

The cause of vapor binding is thereforethe presence or production ofvapor in the liquid in the pump, but this does not completely explainwhat takes place in a turbine pump when it vapor binds. Because itspumping elements consist of a series of buckets and vanes in theperiphery or in the face or faces of the impeller, which elements rotatein an annular channel or raceway interrupted by a liquid block or stop,and because these rotating elements are travelling at relatively highperipheral speeds, the lower inertia of the vapor allows it to fill thebucketsbetween the vanes, displacing the liquid, ,and effectivelypreventing liquid from entering the buckets unless there is a positiveforcel available at the suction of the pump (such as adequate suctionhead) to compress the vapor sufficiently to initiate the pumping action.Once the pumping action is initiated, the compression of the vaporproceeds rapidly, as the pump builds up pressure in the annular channel,until the vapor is condensed or delivered to the pump discharge.

Attempts have been made to improve turbine pumps in this respect byconstructing the suction entrance of the pump in a way to allow` thefull weight of staticsuction head to force the liquid'into the suctionof the pump under sufficient pressure to prevent the pump from vapo-rbinding. In practice, however, improvements of this sort have not beenadequate.

The present invention resides essentially in the combination of acentrifugal pump lirst stage andV a turbine pump second stage, andutilizes the following characteristics of both types of pumps: i

A. The centrifugal stage is usedias the iirst stage, because: (l) Itspumping action is not regenerative, and the exterior of the impeller issmooth; therefore it does not add appreciable heat to the pumped liquid.(2) The centrifugal pump does not carry any liquid over from the highpressure discharge tothe low pressure suction in the imp'eller elementsthemselves (as does a1turbine impeller). (3) The centrifugal pump doesnot produce high discharge pressures in a single stage,so that whateverleakage takes place between the discharge and suction areas is small inproportion to the capacity of the pump. (4) The centrifugal pump willhandle large quantities of vapor providing there is a static suctionhead available. The centrifugal pump is at least as eiiicient(horsepower consumption vs. horsepower output) as a tur-bine pump underall operating conditions.

B. Because of the above characteristics of the centrifugal pump andbecause it operates effectively at the same rotative speeds with similarimpeller diameters as the turbine pump, the centrifugal pump stagedelivers to the turbinepump stage liquid at sufficiently high dischargepressures to effectively prevent, under all reasonable conditions, vaporbinding of the turbine stage.

C. The turbine pump is used as the second stage because: (l) Itsregenerative pumping action produces high pressures in va single stagel0to 2O times the pressure of a centrifugal impeller of the same diameterrotating at the same speed. (2) There being no metal-to-metal contact inthe rotating parts of a turbine pump, a turbine pump can handlelubricating or non-lubricating liquids without wear. the same rotativespeeds as the centrifugal pump.

At least one form of pump with a centrifugal first stage and a turbinesecond stage, as previously proposed for a different purpose, would notbe suitable for the purpose for which the present invention is provided,because it has a leakage patch between a relatively high pressure areaofthe turbine stage and the low pressure area in the suction entrance ofthe centrifugal stage of the pump. Even with a sealing surface alongthis leakage path, the normal wear occasioned by the presence ofabrasive particles in the pumped liquid would soon open up such asealing surface to the point where the superheated liquid from theturbine stage, which .leaks across this sealing surface, would produceso much vapor that the centrifugal stage would vapor bind completely andstop the pumping action.

In the aforementionedfprior form of pump the construction is alsosignificantly different in that the centrifugal impeller and turbineimpeller are arranged in a manner that would not suice for the purposeof the present invention. The size of the suction entrance of thecentrifugal impeller of such pump is limited by the inside diameter of asealing surface inside the vanes and annular channel. suction entranceof` a pump for the purpose for which the pump of the present inventionis provided, should be unusually large to handle satisfactory volumes ofliquid and vapor.

One of the main-objects of the present invention is to -provide animproved combination centrifugal-turbine pump in which there is coactiveutilization of the characteristics of both -types of pumps, and in whichthe arrangement is such that there can be no direct leakage between arelatively high pressure area of the turbine stage and the low pressurearea in the suction entrance ofthe centrifugal stageof the pump.

Another object is to provide an arrangement of the centrifugal andturbine stages of the pump in which sealing surface means is providedfor restraining leakage of the high pressure liquid from the turbinestage and wherein any liquid that does leak from the turbine stage,passes to an area of the centrifugal stage which is under the pressureof the centrifugal force generated there, which effectively prevents theliquid from flashing into vapor.

Another object is'to` provide an arrangement in which the only leakagethat can occur into the suction entrance of the centrifugal first stageis from the discharge of this stage. Because the differential pressuresgenerated in this stage are small relative to the capacity, and sincethe centrifugal impeller itself adds little heat to the liquid, thepossibility of vapor binding this stage is minimal,

This is a serious defect, because the and takes place only under extremeconditions not l usually encountered in actual practice, such asattempt- (3) The turbine pump operates best at ing to operate the pumpat terminal or shutoff pressure while handling a boiling liquid.

Another object is to provide an arrangement of the centrifugal andturbine stages of the pump which will not limit the size of the suctionentrance of the centrifugal stage, but will permit the suction entranceof the centrifugal stage to be unusually large so as to handlesatisfactory volumes of liquid and vapor.

Further objects and advantages of the invention will appear from thefollowing detailed description, taken in connection with theaccompanying drawings which show the construction and operation of anillustrative embodiment of the invention.

In the drawings:

Figure l is a longitudinal sectional view taken substantially along thelines 1--1 of Figure 2;

Figure 2 is a transverse sectional view taken along the line 2-2 ofFigure l;

Figure 3 is a transverse sectional view through the centrifugal impellertaken along the line 3-3 of Figure 1; and

Figure 4 is a fragmentary detailed section showing another sealingarrangement for sealing olf relativelyhigh pressure liquid at the centerof the turbine stage from escaping into the lower pressure centrifugalstage.

Referring to the drawings for a more detailed description, the pumpselected for illustration is a combination centrifugal-turbine pumphaving a pump casing designated in its entirety by the numeral 1. Thecasing y1 comprises a casing part 2, a pair of casing parts 3 and 4 anda sealing ring or annular casing 5 closely surrounding the cylindricalsurfaces 6 and 7 of the casing parts 3 and 4Q The pump shaft S projectsthrough the pump casing part 4, which contains a stutiing box 9 or othersuitable sealing means; also through the casing part 3 and into thecasing part 2. The pump shaft S is driven by any suitable or preferredprime mover (not shown), and the casing extension 10 may be providedwith suitable bearings (not shown) for supporting the shaft 8, and, ifdesired, with a supporting base. A turbine impeller 11 is fixed, forexample, by a key or spline 12 or the like to rotate with the shaft 8. Acentrifugal impeller 13 coaxial with and spaced axially from the turbineimpeller 11 is also fixed, for example, by a key or spline 14, or thelike, to rotate with the shaft 8.

The turbine impeller 11 has at its outer peripherytwo sets of vanes orblades and buckets 15 cut into its opposite sides at the peripherythereof. One set of these vanes 1S opens from one side of the outermarginal portion of the impeller 11, and the other set of vanes 1.5opens from the other side of the outer marginal por- .tion of theimpeller. Both sets of vanes open radially .from the Iouter periphery ofthe impeller 1 1, and both sets of vanes operate in an annular liquidchannel `16 during the rotation of the impeller 11.

The casing parts 3 and 4 have opposed generally annular ribs or anges f7between which the impeller 11 is accurately and closely spaced, or whichabut or cooperate with the opposite sides of the impeller 11 to formsealing surfaces 18 which prevent most of the pressurized liquid fromescaping from the discharge of the annular channel 16 radially inwardlybetween the casing parts 3 and 4 and the opposite lsides of the impeller11. The liquid channel 16 is interrupted by stop o-rv block members 19which may be formed integral with the casing parts 3 and i and preventthe pressurized liouid from escaping to the suction of the turbine stageof the pump from the discharge of the annular channel The centrifugalimpeller i3 which, as already set forth, rotates with the shaft 8 andthe turbine impeller 1l is preferably of the enclosed type as shown moreindetail in Figures l and 3. It has an annular hub20 integral with itswall 21 and an annular hub 22 integral with its wall 23. The hub 20defines the suction inlet Z4 of the centrifugal stage of the Pump andwith the arrangement described this suction inlet opening 24 is notlimited in size but may be as large as desired. This is an importantpractical advantage, because the suction entrance of this type of pumpshould preferably be unusually large to handle satisfactory volumes ofliqui and vapor. i

The hub 20 rotates within a bushing 25 which lines the inner end of theopening inthe hub 26 of the casing part 2. The bushing 25 provides asealing surface around the suction opening 24 to prevent the escape ofliquid from the discharge of the volute channel 27 to the suction inlet24 of the centrifugal stage of the pump. The hub 22 of the centrifugalimpeller 13, along with the hub 28 of the turbine impeller 11, rotateswithin a bushing 30 which seals off relatively high pressure liquid atthe center of the turbine stage from escaping into the lower pressuredischarge of the centrifugal stage.

The construction for sealing the relatively high pressure liquid at thecenter of the turbine stage from escaping into the lower pressuredischarge of the centrifugal stage may be altered in various ways withinthe scope of the present invention. For example, as shown in Figure 4,the shaft 8 itself, which corresponds with the impeller shaft previouslydescribed, may project through a hole or bushing `30 between the twostages to prevent the high pressure liquid from escaping to a lowerpressure portion of the pump. Other parts of Figure 4, which are similarto parts shown in Figures l-3, are designated by primed referencecharacters corresponding to those used in Figures l-3.

The suction inlet 24 of the centrifugal ,stage opens into the spacesbetween the walls 21 and 23 and the enclosed blades 32 of the impeller13 and these spaces open radially outwardly to the volute channel 27.The volute channel 27 opens into the suction entrance 34 of the turbinestage of the pump. The discharge of the annular channel 16 of `theturbine stage delivers the pressurized liquid to the pump outlet 35which thus opens from the discharge of the annular channel 16.

The casing part which, as already set forth, surrounds or encircles thecasing parts 3 and 4 fits between" a flange 38 on the casing part 2 anda flange 40 on the casing part 4 and the casing parts are securedtogether, for example, by screws or bolts 42. The impeller 13 is securedin place on the adjacent reduced diameter end of the shaft 8 by a nut 45between which and the adjacent wall of the impeller 13 a washer 46 isinterposed.

In the operation of the pump, the liquid enters the suction entrance 24of the centrifugal impeller 13 and is discharged from the periphery ofthis impeller into thel volute channel 27 at increased pressure andhigher velocity. Under the pressure of the centrifugal force of the rststage the liquid passes through the suction entrance 34 into the annularliquid channel 16 of the turbine stage. The regenerative pumping actionof the turbine impellerll builds `up sufficient pressure to deliver theliquid to the outlet 35 of the turbine stage, by constant recirculationof the liquid through the` impeller vanes and annular channel 16.

Since the liquid in the suction entrance of the turbine second stage isalways under the pressure of the centrifugal force from the centrifugalfirst stage, vaporization cannotoccur, and this stage will not vaporbind. Further, it has been found that the centrifugal type pump, whenproperlydesigned for handling liquids at or near the boiling pointandoperating with a static suction head, will itself not vapor bind exceptat terminal or shutoff pressure, because, since there is norecirculation ofthe liquid and because of the smooth exterior of theimpeller, very little heat is added to the pumped liquid. Since thesecond stage will not vapor bind if the rst envases stage does notfvapor bind, and sinceunder all pumping conditions the first stage willnot, it isv evident `the complete device as described will not vaporbind.

It `will be apparent from the foregoing descriptionthat the combinationcentrifugal-turbine pump of the present invention coactively utilizesthe characteristics of both types of pumps and that the arrangementissuch that there can be no direct leakage between areas of suiicientdifferential pressure to vapor bind or stop `the pump. The high pressureliquid from the turbine sec ond stage is first restrained along radialpaths by the sealing surfaces 18 and the opposite sides of the turbineimpeller 11 inwardly of the vanes 15. Whatever liquid may leak by thesealing surfaces 18 is restrained from leaking to the centrifugal stageby the sealing surface ,around the hubs 22 and 28 of the centrifugal andturbine impellers 13 and 11, and between these hubs and the bushing 30in Figure l, or between the shaft 8' and the bushing 30' in Figure 4.Even then such liquid as may leak to the centrifugal stage is stillunder the discharge pressure of the centrifugal stage or the centrifugalforce generated there, which effectively prevents the liquid fromflashing into vapor.

The only leakage into the suction entrance 24 of the centrifugal firststage which can occur is from the discharge of the centrifugal stageacross the sealing surface around the hub 20 of the centrifugal impeller13 as provided by the bushing `25. Because the differential pressuresgenerated in the centrifugal stage are small relative to the capacity,and since the centrifugal impeller 13 itself adds little heat to theliquid, the possibility of vapor binding this stage is minimal, and, aspreviously set forth, takes place only under extreme conditions notusually encountered in actual practice, such as attempting to operatethe pump at terminal or shutoff pressure while handling a boilingliquid.

The structural arrangement described does not limit the sizeof thesuction entrance 24 of the centrifugal stage of the pump, but enablesmaking this suction entrance 24 unusually large or, at least, as largeas desired to handle satisfactory volumes of liquid and vapor for thepurposes contemplated.

The use ofthe pump of the present invention is not limited to handling aparticular liquid or particular class of liquids; but the pump may beemployed for pumping any liquids at or near the boiling point.

The centrifugal impeller provided in the` pump of the present inventionis of special type of low volumetric efciency and very low pressurecreating characteristic. Since maximum discharge head of l0 feet at 1750R. P. M., and 20 feet at 3500 R. P. M. is required all otherconsiderations have been sacrificed to the need of pumping boilingliquid with 1 foot or less suction head.`

To this end the special features of the centrifugal impeller are asfollows:

(l) Disproportionately large suction entrance about `50% of the fullimpeller diameter.

(2) Shrouded impeller eye machined inside and outside to a very thinwall.

(3) Deep blades at the impeller eye parabolic with reference to theradius and helical with reference to the aXIS.

(4) A rapid but even volumetric closure of the impeller cavity at theperiphery.

(5) Streamlining of all surfaces in contact with the liquid stream.

By the foregoing means I provide a. centrifugal impeller of specialdesign for developing heads up to l0 feet at V1750 R. P. M. and up to 20feet at 3500 R. P. M. in capacities up to 200 G. P. M specifically foruse in conjunction with the turbine impeller at the above speeds to takeboiling liquids, volatile liquids or liquied gaseswith suction heads oflfoot or less and produce discharge heads up to 800 feet per turbinestage. t

` yThe claims of the present application are not` limited autres to acombination centrifugal-.turbine pump with a centrifugal stage and asingle turbine stage butare of a scope to lcover a centrifugal-turbinecombination with two or more lturbinestages arranged in series (ortandem).

The embodiments of the invention shown inthe drawings are forillustrative purposes only, and it is to be expressly understood thatthe drawings and the accompanying specification are not to be construedas a definition ofthe limits or scope of the invention, reference beinghad to the appended claims for that purpose.

I claim:

1. A centrifugal-turbine pump capable of pumping liquids and liquifiedgases at or near the boiling point thereof with suction heads notgreater than about 1 foot, comprising a pump casing having a firstpumping chan# nel and a second pumping channel disposed laterally ofsaid first pumping channel, a driving Shaft disposed axially o f saidpumping channels, a high pressureregenerative turbine impeller fixed forrotation at all times and in the `same direction with said driving shaftand having peripheral varies forming liquid-propelling buckets inopposite sides of the periphery of said turbine impeller and openingperipherally therefrom, said second pumping channel extending generallyannularly about and spaced outwardly from the periphery of said turbineimpeller so that the liquid Will enter the buckets at both sides of saidturbine impeller and be circulated peripherally into and out of saidbuckets for almost a full revolution of said turbine impeller, saidsecond pumping channel having a discharge outlet opening generallyradially from one end L thereof, said casing having block meansseparating the discharge outlet end of said secondpumping channelannularly from said first pumping channel, said casing having a suctionentrance for the turbine stage opening laterally from said first pumpingchannel to said other end of said second pumping channel, and acentrifugal impeller of low volumetric eliiciency and low pressurecreating characteristics fixed .for rotation within said first pumpingchannel and at all times and in the same direction with said drivingshaft and said high pressure regenerative turbine impeller, saidcentrifugal impeller having a large diameter axial suction inlet eye ofsubstantially the same diameter as a suction inlet for the centrifugalstage defined by said casing and closed blades spaced inwardly from theperiphery of said first pumping channel. so that liquid entering saidsuction inlet eye will be thrown out by centrifugal. force into saidfirst pumping channel and pass 'through the ysuction entrance for theturbine stage into said other end of said second pumping channel toprevent vaporfformation within the pump and provide a mechanicalequivalentto the minimum suction head at which thc rcgenerative turbineimpeller yis operable without vapor binding.

2. In a rotary pump for pumping liquids and `liquified gases at or nearthe boiling pointA thereof, a high pressure regenerative turbineimpeller having peripheral varies forming liquid-propelling buckets inopposite sides of the periphery thereof and opening peripherally fromsaid tur- -turbine impelle'r'to produce a regenerative pumping actionand high pressures, said turbine impeller having an annular wallseparating said liquid-'propelling buckets on one side of said impellerfrom said liquid-propelling buckets on the opposite side of saidimpeller, a centrifugal impeller of low volumetric efiiciency and lowpressure creating characteristics positioned ahead of said turbineimpeller with respect to the direction of movement of the liquid throughthe pump and fixed to turn at all times in the same direction Vandat thesame rotative speeds. as said turbine impeller, acasing havingl a firstpumping channel for said centrifugal limpeller and provided with a largediameter axial suction inlet for the centrifugal impeller and a singleperipheral outlet, said casing having a second pumpchannel extendinggenerally annularly about and spaced outwardly from the periphery ofsaid turbine impeller .SQ that the liquid will cater the buckets 'atboth i sides of said turbine impeller and be circulated periph? erallyinto and out of said buckets for almost a full revolution of saidturbine impeller, said second pumping channel having a peripheralsuction entrance in communication with the single peripheral outlet ofsaid first pumping channel and a single vertical dischargey outlet, andblock means separatingsaid discharge outlet of said second pumpingchannel annularly from said peripheral suction entrance of said secondpumping channel. Y

3. A rotary pump according to claim 2 wherein the block means separatingthe discharge outlet of said second pumping channel from `the suctionentrance of said second pumping channel is integral with the interior ofsaid casing and extends generally radially inwardly therefrom betweenthe discharge outlet and the peripheral suction entrance of said secondpumping channel.

4. A rotary pump according to claim 2 wherein the centrifugal impellerhas closed blades constructed parabolically with reference to the radiusand spirally with reference to the axis thereof.

5. A rotary pump according to claim 2 wherein the turbine impeller andthe centrifugal impeller have oppositely extending tubular hubs whichabut one another and through which a driving shaft connected to turnsaid turbine and centrifugal impellers therewith extends with one end ofsaid shaft terminating at about the inner surface of a radial wallforming a part of a closure for the blades of the centrifugal impeller,and a nut coacting with said radial wall of said centrifugal impellerand screwed axially into the adjacent end of said shaft for securing thecentrifugal impeller in place on said shaft.

6. A rotary pump according to claim 2 wherein the axial suction inletfor the first pumping channel is about half the size of the rotordiameter of the centrifugal im peller.

7. A rotary pump according to claim 2 wherein there are annular ribsintegral with the interior of the casing and cooperating with oppositesides of the turbine impeller radially inwardly of the liquid-propellingbuckets in the periphery thereof for preventing liquid from movingradially inwardly of the turbine impeller.

8. A rotary pump according to claim 2 wherein the turbine impeller andthe centrifugal impeller have oppositely extending tubular hubs whichabut one another and through which a driving shaft connected to turnsaid turbine and centrifugal impellers therewith extends with one end ofsaid shaft terminating at about the inner surface of a radial wallyforming part of a closure for the blades of the centrifugal impeller, anut coacting with said radial wall of said centrifugal impeller andscrewed axially into the adjacent end of said shaft for securing thecentrifugal impeller in place on said shaft, and an annular bushingsurrounding the oppositely extending tubular hubs of the turbine andcentrifugal impellers and cooperating with said casing to seal, thefirst and second pumping .Channels from 01.1@ another.

References Cited in the 'rile of this patent UNITED STATES PATENTS1,875,419 Claypool Sept. 6, 19.32 1,879,803 Johnson Sept. 27, `19321,912,452 Hollander' June 6, 1933 2,055,587 Pigott Sept. 29, 19362,190,245 `Sartell Feb. 13, 1940 2,272,469 Lannert Feb. 10, 19422,374,122 Nelson Apr. 17, 1945 2,468,246 Thayer Apr. 26, 1949 2,601,828Lobanolf July 1, 1952 2,765,748 Buchi Oct. 9, 19,56

FOREIGN PATENTS 513,423 Belgium Aug. 30, 1952 641,391 GreatBritainAugf9,A 195.0 654,854 Great Britain A July 4, 1951 711,791 germany..J-s-l.. Qt- 7. 1.9.4.1

